Low noise variable gain amplifier

ABSTRACT

The present invention provides systems and methods for asymmetrically varying gain in a low noise amplifier. The amplifier includes a first stage amplifier, a plurality of second stage amplifiers coupled to the first stage amplifier, a comparator coupled to one of the second stage amplifiers, and a controller coupled to the comparator, the first stage amplifier, and the plurality of second stage amplifiers. The controller is configured to produce one or more gain control signals to change the gain of one of the first stage amplifier or the plurality of second stage amplifiers at a plurality of asymmetric rates so as to cause the power of the output signal to move toward one of the threshold values of the comparator. The rate of change of the gain is based on conditions including the gain of the first stage amplifier, gain of a second stage amplifier, and the sampled power level.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 60/639,961, filed Dec. 30, 2004, which is incorporatedherein by reference in its entirety.

FIELD OF THE INVENTION

The present invention generally relates to low noise amplifiers (LNA)assemblies and components thereof, gain control in such assemblies, andapplications of the same.

BACKGROUND

In terrestrial digital television (DTV) applications, the receivedsignal is not always direct. For example, the received DTV signal may bereflected by objects, geographic features (e.g., mountains), or may beaffected by weather conditions. As a result, unlike cable TV signals,DTV signals are subject to large drops in the received signals, referredto as fading.

In addition, DTV low noise amplifiers typically have requirements thatexceed the requirements of cable TV low noise amplifiers. For example, aDTV low noise amplifier typically requires more gain, a lower noisefigure, and needs to handle relatively strong adjacent channels. Off-airDTV signals can vary widely in terms of received power level and cancome in quite strongly. In some cases, the desired channel is very weak,and can have a very strong adjacent channel, for example, at a level of40-50 dB stronger than the desired signal.

Accordingly, what is needed is an amplifier that can rapidly adapt tosignals with large amounts of fading.

What is further needed is a system that can selectively respond fasteror slower to a detected power level and achieve a linear type ofresponse while still providing benefits of digital gain control fordownstream power management.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate the present invention and, togetherwith the description, further serve to explain the principles of theinvention and to enable a person skilled in the pertinent art to makeand use the invention.

FIG. 1 is a block diagram of an exemplary low noise amplifier, accordingto an embodiment of the present invention.

FIG. 2 is a block diagram of an exemplary window comparator.

FIG. 3 is an example plot of detected power signal versus time for anexemplary amplifier having a five level comparator.

FIG. 4 is a flowchart of an example method in a controller forcontrolling the gain of a first stage amplifier and the gains of aplurality of second stage amplifiers.

FIG. 5 is an example method in a controller for increasing gain.

FIG. 6 is an example method in a controller for decreasing gain.

The present invention will now be described with reference to theaccompanying drawings. In the drawings, like reference numbers canindicate identical or functionally similar elements. Additionally, theleft-most digit(s) of a reference number may identify the drawing inwhich the reference number first appears.

DETAILED DESCRIPTION OF THE INVENTION

1.0 Overview

Low noise amplifiers often include a two-stage amplifier with a firststage having a relatively higher, variable, gain than one or more secondstage amplifiers. A power detector coupled to an output of the DTV lownoise amplifier drives an automatic gain control (AGC) circuit, whichsets the gain of the low noise amplifier to maintain a fixed outputlevel. The AGC level can be set to a range of values by a digitalinterface circuit. In an exemplary embodiment, the first stage amplifierprovides a variable gain of, for example, 15 dB and the second stageamplifier provides a variable gain of, for example, 12 dB. In thisexample, the system has a total gain of approximately 27 dB, and an AGCrange of approximately 50 dB. As would be appreciated by persons ofskill in the art, other gains could be used for the first and secondstage amplifiers.

2.0 Structural Embodiments of the Present Invention

FIG. 1 is a block diagram of an exemplary low noise amplifier 100. Lownoise amplifier 100 and/or portions thereof can be used in cabletelevision applications (e.g., NTSC, digital TV and/or cable modem) orin terrestrial analog (NTSC) or digital television (DTV) applications.When implemented in a DTV application, the present invention is referredto herein as a DTV low noise amplifier. Low noise amplifier 100, orportions thereof, can also be used as a variable gain low noiseamplifier for an off-air DTV receiver.

Low noise amplifier 100 includes a first stage variable gain amplifier110, a gain control module 120, and a plurality of second stageamplifiers 130 a-n constructed on an integrated circuit (IC) substrateor chip 103. Low noise amplifier 100 also includes various additionalelements internal or external to chip 103.

First stage variable gain amplifier 110 is coupled to gain controlmodule 120 and to the plurality of second stage amplifiers 130 a-n.First stage variable gain amplifier 110 is a differential amplifierhaving differential inputs and differential outputs. First stageamplifier 110 receives input signal 102 over differential signal lines150 a and 150 b. Amplifier 100 receives the input signal via an antenna(e.g., antenna 185 depicted in FIG. 1) or a cable (not shown). Thereceived signal is then fed through an optional balun 180 to producedifferential signal 102. Antenna 185, cable input (not shown), and balun180 are off-chip.

In addition, first stage amplifier 110 receives a plurality of gaincontrol signals 122 from controller 126. First stage amplifier 110amplifies input signal 102 according to the gain of the first stageamplifier which is determined by the received gain control signals 122.Amplifier 110 then produces an amplified signal 112 and transmitsamplified signal 112 via differential signal lines 155 a and 155 b tothe plurality of second stage amplifiers 130 a-n. Second stageamplifiers 130 a-n are arranged such that each amplifier 130 receivessignal 112 in parallel and at the respective differential inputs of eachsecond stage amplifier 130 a-n.

First stage amplifier 110 is an impedance matched variable gain lownoise amplifier using shunt feedback. For a detailed description of animpedance matched variable gain low noise amplifier using shuntfeedback, see U.S. Provisional Patent Application No. 60/635,174,entitled “Impedance Matched Variable Gain Low Noise Amplifier”, which isherein incorporated by reference in its entirety.

Each second stage amplifier 130 also has a programmable gain. Thus,second stage amplifiers 130 a-n are also variable gain amplifiers. Eachsecond stage amplifier 130 is coupled to controller 126. Each secondstage amplifier 130 amplifies signal 112 by its respective gain toproduce an output signal 192. Second stage amplifiers 130 a-n aredifferential amplifiers. Thus, output signal 192 is a differentialsignal.

Gain control module 120 is coupled between the output of one of theplurality of second stage amplifiers 130 (e.g., amplifier 130 n) andfirst stage amplifier 110. Gain control module 120 includes a powerdetector 160, a comparator module 140, controller module 126, and aclock oscillator 128.

Power detector 160 includes a power detection module 162, a capacitor164, and an optional resistor 166. Capacitor 164 and optional resistor166 may be located off-chip. Capacitor 164 and resistor 166 are coupledbetween the output of power detection module 162 and ground. Powerdetection module 162 receives differential output signal 192 from one ofthe plurality of second stage amplifiers 130 (e.g., output signal 192n). Power detector 160 is configured to detect the power level ofreceived output signal 192 and to communicate the detected power levelto comparator module 140 via a signal 194. As would be appreciated bypersons of skill in the art, other methods to detector the power levelcan be used with the present invention.

Comparator module 140 includes a window comparator 170 and a pluralityof threshold registers 142 a-n. Threshold registers 142 a-n provide thethresholds against which the detected power level is compared. In anembodiment, threshold registers 142 a-n are digital to analog converters(DACs).

Comparator 170 receives detected power level signal 194 at a comparisoninput. Comparator 170 then compares power level signal 194 against theplurality of thresholds to produce comparison signals 196 a-n.Comparison signals 196 a-n indicates where the detected power of outputsignal 192 is relative to the plurality of thresholds of thresholdregisters 142 a-n. Thus, low noise amplifier 100 uses multiple levels ofquantization. This allows the low noise amplifier to respond to changesin the signal level at multiple rates. These rates can be asymmetricallyor symmetrically related to the power level signal 194.

In an embodiment, the output of comparator 170 is an n-level thermometercode. For example, when window comparator 170 includes five comparators,output signals 196 a-n represent a six level thermometer code. However,as would be appreciated by persons of ordinary skill in the relevantart, more comparators could be used in window comparator to produce ahigher number of thermometer codes or the power detector output signalcould be digitized to even more levels with binary code. This producesgreater flexibility and adaptability to the gain control response at theexpense of additional circuitry and power consumption. The use of fiveor more comparators provides an increased ability to respond to signalfading. Two specific benefits result from using multiple comparators.One is that the gain may be caused to change faster in response tolarger errors in output signal amplitude (larger in magnitude, whetherthe signal is too weak or too strong).

The other is asymmetrical response for signals that are too strongversus too weak. This may be desirable so that the AGC adapts to eitherthe maximum or minimum of the fade (typically the maximum), thuspreventing picture disturbances in response to AGC activity.

Controller 126 receives comparison signals 196 a-n and a clock signal198 generated by clock oscillator 128. Controller 126 then generates aset of gain control signals 122 and 124. Gain control signals 122 areconfigured to set the gain of first stage amplifier 110. Gain controlsignals 124 are configured to set the gains of second stage amplifiers130 a-n. In addition, controller 126 provides a comparator controlsignal 175 to comparator 170. At periodic intervals, controller 126asserts comparator control signal 175 causing comparator 170 to producecomparison signal 196. The periodic time intervals may be programmablein duration and correspond to the rate at which the power level of inputsignal 102 is expected to vary. Controller 126 may also providethreshold values to threshold registers 142 a-n. Controller 126 isoptionally connected to an external controller (not shown).

Amplifier 100 may include an optional decoder and switch matrix (notshown) between controller 126 and amplifier 110. For a more detaileddiscussion of a decoder and switch matrix, see U.S. patent applicationSer. No. 10/822,729, entitled “Gain Control Methods and Systems in anAmplifier Assembly,” which is herein incorporated by reference in itsentirety.

FIG. 2 is a block diagram of an exemplary window comparator 270. In theembodiment of FIG. 2, window comparator 270 includes five thresholdcomparators. However, additional comparators can be used with thepresent invention.

Comparator 270 includes first upper threshold comparator 272 forcomparing power level signal 294 to upper threshold B. First upperthreshold comparator 272 produces a result 244 a indicative of whetherdetected power level signal 294 is higher or lower than upper thresholdB. Comparator 270 includes a second upper threshold comparator 274 forcomparing power level signal 294 to upper threshold A. Second upperthreshold comparator 274 produces a result 244 b indicative of whetherdetected power level signal 294 is higher or lower than upper thresholdA. Comparator 270 includes an optimum threshold comparator 276 forcomparing power level signal 294 to an optimum threshold. Optimumthreshold comparator 276 produces a result 244 c indicative of whetherdetected power level signal 294 is higher or lower than the optimumthreshold. Comparator 270 includes a first lower threshold comparator280 for comparing power level signal 294 to lower threshold B. Firstlower threshold comparator 280 produces a result 244 e indicative ofwhether detected power level signal 294 is higher or lower than lowerthreshold B. Comparator 270 includes a second lower threshold comparator278 for comparing power level signal 294 to lower threshold A. Secondlower threshold comparator 278 produces a result 244 d indicative ofwhether detected power level signal 294 is higher or lower than lowerthreshold A.

FIG. 3 is an example plot of detected power signal 194 versus time foran exemplary amplifier having a five level comparator, such as depictedin FIG. 2. The example plot of FIG. 3 serves as a useful illustration ofthe operation of first stage amplifier 104 with respect to detectedpower signal 194 and thresholds 244 a-e. In the example illustrated inFIG. 3, six levels (or ranges) are created by comparator 270.

For example, when the detected power signal is above upper limit B(i.e., in level A), the thermometer code output 196 of the comparator is11111. When the detected power signal is between upper limit B and upperlimit A (i.e., in level B), the output 196 of the comparator is 01111.When the detected power signal is between optimum threshold and upperlimit A (i.e., in level C), the output 196 of the comparator is 00111.When the detected power signal is between the optimum threshold andlower limit A (i.e., in level D), the output 196 of comparator 270 is00011. When the detected power signal is between lower limit A and lowerlimit B (i.e., in level E), the output 196 of comparator 270 is 00001.When the detected power signal is below lower limit B (i.e., in levelF), the output 196 of comparator 270 is 00000.

An initial assumption is that at a time to, the power of input signal102, the gain of amplifier 110, and the resulting power of signal 192are such that detected power level 194 is in level C (i.e., betweenoptimum threshold and upper limit A), as depicted in FIG. 3. It is alsoassumed that at periodic time intervals, controller 126 samplescomparison signal 196. Beginning at time to, a slow increase in thepower of input signal 102 causes a correspondingly slow increase inoutput signal 192 and detected power level signal 194. Controller 126maintains the gain of amplifier 104 at a fixed level. Eventually, powerlevel signal 194 rises to a level between upper threshold A and upperthreshold B. At the next sample time 352, comparator 270 transmits code01111 to indicate that the power level is now in level B. In response,controller 126 generates gain control signals to decrease the gain ofamplifier 110 continuously and smoothly and correspondingly detectedpower level signal 194 decreases until the power level signal passesbelow the optimum threshold.

3.0 Method of Operation

FIG. 4 is a flowchart of an example method 400 in controller 126 forcontrolling the gain of the first stage amplifier 110 and the gains ofthe plurality of second stage amplifiers 130. Method 400 begins at step402 when controller 126 is reset.

In step 404, controller 126 initializes the chip.

In step 406, controller 126 samples comparator 170. This step involvespolling comparator 170 (e.g., sending comparator control signal 175),causing comparator 170 to transmit comparison signal 196.

In step 410, a determination is made whether the received comparisonsignal 196 indicates that the detected power level is in one of the lowlevels identified for correction. As described above, the number oflevels available is based on the number of comparators used in windowcomparator 170. For example, when the window comparator has fivecomparators, six levels are available. One or more of the levels areidentified as low levels needing correction. For example, in FIG. 3.,levels E (00001) and F (00000) may be identified as levels wherecorrection is necessary. If the detected power level is in one of thelow levels identified for correction, the operation proceeds to step415. If the detected power level is not in one of the low levelsidentified for correction, the operation proceeds to step 420.

In step 420, a determination is made whether the received comparisonsignal 196 indicates that the detected power level is in one of the highlevels identified for correction. One or more of the levels areidentified as high levels needing correction. For example, in FIG. 3.,levels A (11111) and B (01111) may be identified as levels wherecorrection is necessary. If the detected power level is in one of thehigh levels identified for correction, operation proceeds to step 425.If the detected power level is not in one of the high levels identifiedfor correction, operation proceeds to step 430.

In step 415, the gain of the low noise amplifier is increased. In thisstep, the gain is increased at one of a plurality of rates. The rate ofincrease is determined based on one or more of the following: the gainof the stage one amplifier, the detected power level, and/or the gain ofthe stage 2 amplifier. Step 415 is described in greater detail below inreference to FIG. 5.

In step 425, the gain of the low noise amplifier is decreased. In thisstep, the gain is decreased at one of a plurality of rates. The rate ofdecrease is determined based one or more of the following: the gain ofthe stage one amplifier, the detected power level, and/or the gain ofthe stage 2 amplifier. Step 425 is described in greater detail below inreference to FIG. 6.

In step 430, the controller waits a period of time. At the end of thisperiod, operation returns to step 406. The wait period may beprogrammable.

Controller 126 can increase the gain in step 415 at the same rate atwhich the gain is decreased in step 425. In an alternate embodiment, thecontroller can increase and decrease the gain asymmetrically (e.g., atdifferent rates). For example, controller 126 may increase gain at afaster rate that the gain is decreased. This causes the AGC of the lownoise amplifier to behave more like a peak detector in response tofading.

FIG. 5 is an example method 500 in controller 126 for increasing gain(step 415). Method 500 begins at step 502.

In step 504, a determination is made whether the gain of first stageamplifier 110 is greater than or equal to the maximum gain of firststage amplifier 110. If the gain is not greater than or equal to themaximum gain, the operation proceeds to step 510. If the gain is greaterthan or equal to the maximum gain, the operation proceeds to step 506.

In step 510, the gain of first stage amplifier 110 is increased. Therate at which the gain is increased is determined based on the detectedpower level. Step 510 includes steps 512 through 518.

In step 512, a determination of the level of the received compensationsignal 196 is made. If the signal is in a level identified for type 1correction, operation proceeds to step 514. If the signal is in a levelidentified for type 2 correction, operation proceeds to step 516. Forexample, in FIG. 3, the level F (00000) is designated for type 2correction. The remaining levels are then identified for type 1correction.

In step 514, the rate for updating the gain is set to rate 1.

In step 516, the rate for updating the gain is set to rate 2. In anembodiment, rate 2 is faster than rate 1.

In step 518, the gain of stage 1 amplifier 110 is increased.

Although step 510 describes the use of two rates, a person of skill inthe art will recognize that additional rates can be used based on thenumber of levels supported. For example, if four levels are designatedincrease gain processing, a separate rate can be assigned for eachlevel. Thus, up to four rates can be used for increasing the gain.

In step 530, a determination is made whether feedback of first stageamplifier 110 is turned on. This step is optional and is only present iffirst stage amplifier has feedback capabilities.

In step 506, a determination is made whether the gain of second stageamplifier 110 is greater than or equal to the maximum gain of secondstage amplifier 110. If the gain is not greater than or equal to themaximum gain, operation proceeds to step 520. If the gain is greaterthan or equal to the maximum gain, operation proceeds to step 570.

In step 520, the gain of the second stage amplifiers 130 is increased.The rate at which the gain is increased is determined based on thedetected power level. Step 520 includes steps 522 through 528.

In step 522, a determination of the level of the received compensationsignal 196 is made. If the signal is in a level identified for type 1correction, operation proceeds to step 524. If the signal is in a levelidentified for type 2 correction, operation proceeds to step 526. Forexample, in FIG. 3, the level F (00000) is designated for type 2correction. The remaining levels are then identified for type 1correction.

In step 524, the rate for updating the gain is set to rate 1.

In step 526, the rate for updating the gain is set to rate 2, which maybe faster than rate 1.

In step 528, the gain of the plurality of stage 2 amplifiers 130 isincreased.

Although step 520 describes the use of two rates, a person of skill inthe art will recognize that additional rates can be used based on thenumber of levels supported. In addition, step 520 may use the same ratesas step 510 or different rates based on the needs of the application.

In step 540, the comparator is sampled.

In step 550, a determination is made whether comparison signal 196 isabove the optimum threshold. If signal 196 is above the optimumthreshold, operation proceeds to step 570. If signal 196 is not abovethe optimum threshold, operation returns to step 504.

In step 570, operation returns to step 430 of FIG. 4.

FIG. 6 is an example method 600 in controller 126 for decreasing gain(step 425). Method 600 begins at step 602.

In step 604, a determination is made whether the gain of the secondstage amplifiers 130 is less than or equal to the minimum gain of thesecond stage amplifiers 130. If the gain is not less than or equal tothe minimum gain, operation proceeds to step 610. If the gain is lessthan or equal to the minimum gain, operation proceeds to step 606.

In step 610, the gain of the second stage amplifiers 130 is decreased.The rate at which the gain is decreased is determined based on thedetected power level. Step 610 includes steps 612 through 618.

In step 612, a determination of the level of the received compensationsignal 196 is made. If the signal is in a level identified for type 3correction, operation proceeds to step 614. If the signal is in a levelidentified for type 4 correction, operation proceeds to step 616. Forexample, in FIG. 3, level A (11111) is designated for type 4 correction.The remaining levels are designated for type 3 correction.

In step 614, the rate for updating the gain is set to rate 3.

In step 616, the rate for updating the gain is set to rate 4 which maybe faster than rate 3.

As described above, rates 1 and 2 (for increasing the gain) can be equalto rates 3 and 4 (for decreasing the gain). Alternatively, rates 1 and 2can be different than rates 3 and 4.

In step 618, the gain of the second stage amplifiers is decreased.

Although step 610 describes the use of two rates, a person of skill inthe art will recognize that additional rates can be used based on thenumber of levels supported.

In step 606, a determination is made whether the gain of the first stageamplifier 110 is less than or equal to the minimum gain of the firststage amplifier 110. If the gain is not less than or equal to theminimum gain, the operation proceeds to step 620. If the gain is lessthan or equal to the minimum gain, the operation proceeds to step 670.

In step 620, the gain of the first stage amplifier 110 is decreased. Therate at which the gain is decreased is determined based on the detectedpower level. Step 620 includes steps 622 through 628.

In step 622, a determination of the level of the received compensationsignal 196 is made. If the signal is in a level identified for type 3correction, the operation proceeds to step 624. If the signal is in alevel identified for type 4 correction, the operation proceeds to step626. For example, in FIG. 3, level A (11111) is designated for type 4correction. The remaining levels are designated for type 3 correction.

In step 624, the rate for updating the gain is set to rate 3.

In step 626, the rate for updating the gain is set to rate 4 which maybe faster than rate 3.

In step 628, the gain of stage 1 amplifier 110 is decreased.

Although step 620 describes the use of two rates, a person of skill inthe art will recognize that additional rates can be used based on thenumber of levels supported.

In step 630, a determination is made whether feedback of first stageamplifier 110 is turned off. This step is optional and is only presentif first stage amplifier has feedback capabilities.

In step 640, the comparator is sampled.

In step 650, a determination is made whether comparison signal 196 isbelow the optimum threshold. If signal 196 is below the optimumthreshold, operation proceeds to step 670. If signal 196 is not belowthe optimum threshold, operation returns to step 604.

In step 670, operation returns to step 430 of FIG. 4.

4.0 Conclusion

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. It will be apparent to persons skilledin the relevant art that various changes in form and detail can be madetherein without departing from the spirit and scope of the invention.Thus, the breadth and scope of the present invention should not belimited by any of the above-described exemplary embodiments, but shouldbe defined only in accordance with the following claims and theirequivalents.

1. A method for varying gain in an amplifier, comprising: (a) defining aplurality of output level ranges, wherein each of the plurality ofoutput level ranges are defined using a first threshold value and asecond threshold value; (b) increasing the gain of the amplifier by afirst rate when a power level for an output signal of the amplifier iswithin a first output level range; and (c) increasing the gain of theamplifier by a second rate when the power level for the output signal iswithin a second output level range, wherein the first rate is differentthan the second rate; and (d) decreasing the gain of the amplifier by athird rate when the power level for the output signal is within a thirdoutput level range.
 2. The method of claim 1, further comprising thestep of: prior to step (b), sampling the power level of an output signalof the amplifier.
 3. The method of claim 1, wherein the first rate isdifferent than the third rate.
 4. The method of claim 2, furthercomprising: if the sampled power level is below an optimum threshold forthe amplifier, repeating steps (b) and (c).
 5. The method of claim 2,further comprising: if the sampled power level is above an optimumthreshold for the amplifier, repeating step (d).
 6. A method for varyinggain in an amplifier, comprising: (a) sampling a power level of anoutput signal of the amplifier; (b) selecting a gain variation rate froma plurality of gain variation rates based on the sampled power level,wherein each gain variation rate is associated with a predefined outputlevel range and wherein the plurality of gain variation rates includesat least two gain increase rates; and (c) varying the gain of theamplifier according to the selected gain variation rate.
 7. The methodof claim 6, wherein the amplifier includes a first stage amplifiercoupled to a second stage amplifier, and wherein step (b) comprises: (i)selecting a first gain variation rate based on one or more conditionsincluding a first sampled power level, a gain of the first stageamplifier, and a gain of the second stage amplifier; and (ii) selectinga second gain variation rate based on one or more conditions including asecond sampled power level, a gain of the first stage amplifier, and again of the second stage amplifier.
 8. The method of claim 7, whereinstep (b)(i) comprises: selecting the first gain variation rate if thesampled power level is within a range identified for a type 1 increasegain correction and the gain of the first stage amplifier is greaterthan or equal to a first predetermined value; and selecting the firstgain variation rate if the sampled power level is within a rangeidentified for the type 1 increase gain correction, the gain of thefirst stage amplifier is below the first predetermined value, and thegain of the second stage amplifier is greater than or equal to a secondpredetermined value.
 9. The method of claim 8, wherein step (b)(ii)comprises: selecting the second gain variation rate if the sampled powerlevel is within a range identified for a type 2 increase gain correctionand the gain of the first stage amplifier is above or equal to a firstpredetermined value; and selecting the second gain variation rate if thesampled power level is within a range identified for type 2 increasegain correction, the gain of the first stage amplifier is below thefirst predetermined value, and the gain of the second stage amplifier isabove or equal to a second predetermined value.
 10. The method of claim9, wherein the first gain variation rate is different than the secondgain variation rate.
 11. The method of claim 6, further comprising: (d)repeating steps (b) and (c) until the sampled power level falls withinan optimal range.
 12. An amplifier, comprising: a first stage amplifier;a plurality of second stage amplifiers, wherein each second stageamplifier is configured to receive an output of the first stageamplifier; a comparator module coupled to one of the plurality of secondstage amplifiers, wherein the comparator module is configured to comparea detected power of an output signal of one of the plurality of secondstage amplifiers to at least five threshold values, and wherein thecomparator module is further configured to produce an output signalindicative of a level of the detected power signal relative to the atleast five threshold values; and a controller coupled to the comparatormodule, the first stage amplifier, and the plurality of second stageamplifiers, wherein the controller is configured to determine the rateof change of a gain of the first stage amplifier and the rate of changeof a gain of each of the second stage amplifiers, wherein the controlleris further configured to produce a plurality of gain control signals tochange the gain of one of the first stage amplifier or the plurality ofsecond stage amplifiers at a plurality of asymmetric rates so as tocause the power of the output signal to move toward one of said at leastfive threshold values.
 13. The system of claim 12, wherein thecontroller is configured to: increase the gain at a first rate when thecomparator module indicates the detected power level is in a low levelidentified for correction; and decrease the gain at a second rate whenthe comparator module indicates the detected power level is in a highlevel identified for correction.
 14. The system of claim 13, wherein thecontroller is further configured to select the first rate from aplurality of gain increase rates based on one or more conditionsincluding the detected power level, the gain of the first stageamplifier, and the gain of the second stage amplifier.
 15. The system ofclaim 13, wherein the controller is further configured to select thesecond rate from a plurality of gain decrease rates based on one or moreconditions including the detected power level, the gain of the firststage amplifier, and the gain of the second stage amplifier.
 16. Thesystem of claim 12, wherein: the first stage amplifier is a variablegain amplifier having a gain programmable by one or more gain controlsignals; and each second stage amplifier is a variable gain amplifierhaving a gain programmable by one or more gain control signals.